Redundancy protection switching for electronic devices involves switching of activity between a working device and a protection device. The working device and the protection device are typically substantially identical devices, one of which is selected to be active at any time. In a communication network for instance, identical signals are transmitted over a working line and a protection line which connect working line cards and protection line cards in different switches. Although the working line and the working line cards are normally active, operation may be switched to the protection line and the protection line cards in the event of a failure of the working line or one of the working line cards.
This type of device-based protection switching causes all services supported on a working device to be switched to a protection device, and is therefore particularly suited to implementations in which a working device supports only one service, as in the case of a line card having a single interface, for example. However, for such devices as multiple-interface devices which support multiple services, device-based protection switching may unnecessarily switch all services to a protection device when one or more of the services remain operable on a working device. Instead of switching only failing services, some current multiple-interface devices provide only device redundancy and thus switch all device functions when any of the functions require switching.
An alternative protection switching system provides for per-port protection switching for line cards by switching line interface functionality independently of line termination functionality via a system midplane. In this type of system, line interfaces are separate from line cards. This technique is only feasible, however, for line cards having a midplane and separate line interfaces.
As those skilled in the art will appreciate, increasing interface densities in multiple-interface devices may reduce costs, in that resources in a single device may be shared between multiple interfaces. Multiple-interface devices may also provide further advantages, including increasing bandwidth through a switch, for example. Therefore, multiple-interface devices and per-interface protection switching techniques for such devices are becoming more important.